Apparatus for stabilizing paper webs



June 10, 1969 R PAM ET AL 3,448,529

APPARATUS FOR STABILIZING PAPER WEBS Filed July 13, 1965 INVENTORS.AUGUST 8. ERSPAMER WILLIAM R. SHERMAN United States Patent 3,448,529APPARATUS FOR STABILIZING PAPER WEBS August S. Erspamer, Drexel Hill,and William R. Sherman, Chester, Pa., assignors to Scott Paper Company,Delaware County, Pa., a corporation of Pennsylvania Filed July 13, 1965,Ser. No. 471,573 Int. Cl. F26b 13/04; D06c 3/06 US. Cl. 34-416 5 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to the art ofpapermaking and more particularly to apparatus for producing paperhaving improved dimensional stability.

It has long been recognized that paper made from cellulosic fibers has atendency to change dimensions when subjected to varying moistureconditions. For example, a conventional paper web will generallyincrease in length (the direction parallel to the machine direction, ordirection in which the web has been run through a papermaking machine)and in width (the direction parallel to its cross-machine) when themoisture content of the atmosphere ambient the web is increased. Mostpaper webs demonstrate less dimensional stability in the cross-machinedirection than in the machine direction, i.e. the width of the sheetundergoes greater dimensional changes than does the length of the webfor given changes in the ambient atmosphere surrounding the web.Moreover, it has been found practicable to change and/ or control themachine direction dimensional stability of a paper web by varying thelongitudinal tension to which the web is subjected during drying in thepapermaking machine. Control of cross-direction dimensional stabilityhas, however, continued to present a problem for the papermaker.

Certain present day applications require papers exhibiting unusualdimensional stability both in the machine and in the cross-machinedirections. Card stock used, for example, in making punch cards for usein tabulating and computing equipment is required to have a very highdegree of dimensional stability to insure reliable operation of theequipment with which it is used. Up to the present time known methodsand apparatus for controlling cross-machine stability have notsuccessfully produced paper sock with the desired stability for thisapplication.

The principal object of this invention, therefore, is the production ofpaper webs having improved dimensional stability in the cross-machinedirection. This objective is achieved through utilization of an improvedprinciple of straining the web in a cross-machine direction durngpassage of the web through the drying apparatus of a papermakingmachine. Although attempts have been made in the past to stretch paperwebs in a cross-machine direction during manufacture of the paper, suchattempts have not been successful in materially improving thedimensional stability of the webs.

The underlying principles of this invention reside in the disposition ofweb straining devices, such as bowed expander rolls, within the dryingsection, or sections, of a papermaking machine in locations in whichthese devices impart a cross-machine strain to a parallelly dried webice which is immediately thereafter subjected to further drying whilerestrained against cross-machine shrinkage. The invention furthercontemplates disposition of these straining devices in locations whereinmaximum straining effect may be achieved from their use.

More specifically, the invention contemplates a novel arrangement ofbowed expander rolls interspersed among the dryers, or drying drums, ofa papermaking machine.

Further objects, advantages and features of the invention will beapparent from the following detailed description thereof in whichreference is made to the accompanying drawing wherein:

FIG. 1, comprising two parts (1a and 1b), is a schematic elevation viewof a portion of a papermaking machine embodying this invention;

FIG. 2 is an enlarged elevation view of one of the straining devicesemployed in the apparatus of FIG. 1 and,

FIG. 3 is a plan View of the straining device of FIG. 2.

FIG. 1 illustrates the principal components of the drying portion of apapermaking machine in which a wet web, 11, of papermaking fibers passesfrom a Fourdriner Wire 10 running around a roll 12, on which wire theweb has been formed, through a series of press rolls 13 andconsecutively through three dryer sections indicated generally byreference numerals 14, 15 and 16, respectively. A machine of this typemay have a pair of size press rolls 17 interposed between dryer sections15 and 16 and also is equipped with a reel (not shown) for winding thedried web 11 into a roll after it leaves the last dryer section 16.

Each of the dryer sections 14, 15 and 16 includes a plurality of heatedcylindrical dryers, or drying drums, which are mounted for rotation onhorizontal axes. It is conventional practice to arrange such dryers intiers with the dryers of one tier staggered with respect to the dryersin the tier immediately thereabove or therebelow.

The nine dryers in section 14 have been consecutively numbered 21through 29 in the sequence in which the paper web 11 is fed thereover ina conventional papermaking machine. It is to be noted, however, that inaccordance with this invention and as illustrated in FIG. 1, web 11 isnot fed over the dryers in the conventional sequence indicated by thenumbers. The preferred sequence of web feed through the dryers ofsection 14 is 21-22- 24-23-25-27-26-28 and 29. This feed arrangementaccommodates the travel of web 11 to a series of four web strainingdevices, each indicated by reference numera130, which contact the webduring its passage, respectively, between dryers 22 and 24, dryers 23and 25, dryers 25 and 27, and dryers 26 and 28.

Each web starining device 30 preferably consists of a bowed expanderroll of the type illustarted schematically in FIGS. 2 and 3. Expanderrolls of this type are commonly used for spreading and smoothing websand comprise a resilient cylindrical surface rotating about a bowed axisand which may, if desired, be equipped with means (not shown) forchanging the degree of bow of the axis. A roll of this type is describedin greater detail in US. Patent No. 2,960,749 to Robertson et al.,granted Nov. 22, 1960.

Web 11 is caused to pass over each straining device 30 in such a manneras to first contact the surface of the bowed roll at a location to theinside of the bow where the surface of the roll is in a relaxed,unstretched condition and to remain in contact with the surface of theroll to a location near the outside of the bow so as to be subjected toa transverse, or cross-machine, strain by virtue of extension of thesurface of the roll in passing from the inside of the bow to the outsideof the bow (see FIG. 3). In accordance with this invention, the expanderdevices 30 are positioned between and displaced from the center lines ofadjacent dryers over which the web 11 is passing and spaced from thedryer center-lines in a direction opposite the portions of the dryersover which the web passes in order to obtain maximum wrap of the surafceof the devices 30 by the web 11. This preferred relationship between thestraining devices 30 and the dryers is illustrated in FIG. 1 from whichit will be noted that one straining device 30 is disposed between andabove the center lines of dryers 22 and 24 with web 11 passingconsecutively over lower surface regions of these dryers. Similarly,another straining device 30 is positioned be tween, but below, thecenter lines of dryers 23 and 25 because web 11 passes consecutivelyover upper surface regions of the latter two dryers. In each instancethe direction of curvature of the web passing over the two dryers is thesame and opposite to the direction of curvature of the web in passingover the intervening straining device. This positioning of the strainingdevice allows for maximum wrap, preferably in excess of 150 arcuatedegrees, and up to 180 degrees of the surface of the devices 30 by theweb 11. The degree of wrap is shown in FIGURE 2 an an angle of contactdesignated by reference numeral 30a.

It is further to be noted that, in accordance with this invention, thestraining devices 30 are positioned within dryer section 14 so as tofollow passage of web 11 over the initial dryers 21 and 22 of thesection and precede passage of the web over the last dryers, 28 and 29in this section. In these locations the straining devices act on web 11after it has been at least partially dried, so as to impart a ceraindegree of physical integrity to the web, with the result thatcrossmachine direction stretching of the web by devices 30 has theeffect of actually straining the web rather than merely separatingloosely adhered fiber components of the web.

It is also deemed to be important that the web leaving each of thestraining devices 30 be subjected to the restraining action ofconfinement against a dryer surface immediately after leaving eachstraining device. This restraining action is preferably accomplished byconfining the strained web between the next dryer and a traveling dryerfelt, indicated by dotted line 31. Dryer section 14, in accordance withusual dryer practice, employs two felts 31 which pass over the surfacesof the upper and lower tiers of dryers, respectively, and which are heldagainst the dryers by means of rolls 32 positioned between adjacentdryers and at the ends of the dryer section.

It has been ascertained to be of particular importance to allow thestrained web 11 to pass over at least two dryers, such as 28 and 29, tobe further dryed and set before the web passes through any unrestraineddraw such as exists between dryer sections 14 and 15 and in the regionof press rolls 17 between dryer sections 15 and 16.

Dryer sections 15 and 16 preferably contain crossmachine strainingdevices 30 disposed among the several dryers in the same order ofplacement as devices 30 in dryer section 14. Thus, in section 15, inwhich the conventional dryer sequence is indicated by the sequence ofreference numerals 35 through 39, the order of web feed is dryers35-37-36-38 and 39, with straining devices 30 located in contact withweb 11 between dryers 35 and 37 and 36 and 38, respectively. The webpath through dryer section 16 covers in sequence dryers 41, 43, 42, 44and 45 with the straining devices being positioned respectively betweendryers 41 and 43 and 42 and 44. Dryer sections 15 and 16 are bothequipped with felt runs 31 similar to dryer section 14.

From the foregoing it will be apparent that this invention provides anovel arrangement for imparting a transverse strain to a partially driedpaper web and for subsequently setting the strain in the web for thepurpose of improving the transverse dimensional stability of the web.Although the invention has been described in connection with a preferredembodiment thereof it will be apparent to persons skilled in the artthat various changes may be made in the apparatus employed withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. Apparatus for stabilizing a paper web comprising at least two heated,rotatable drums, and means comprising a bowed roll disposed intermediatesaid drums for transversely straining a web passing from one drum to theother drum, the path of travel of said web being such as to undergo thesame direction of curvature around said drums and the opposite directionof curvature around said bowed roll, said roll being bowed in adirection to produce maximum transverse stretching of the Web duringpassage of the web thereover.

2. Appartus for stabilizing a paper web comprising at least two heated,rotatable drums, and means comprising a bowed roll disposed intermediatesaid drums for transversely straining a web passing from one drum to theother drum, the path of travel of said web being such as to undergo thesame direction of curvature around said drums and the opposite directionof curvature around said bowed roll, said roll being disposed in aposition approximately equidistant from the axes of said drums toproduce maximum wrap of the surface of said roll by said web, and saidroll being bowed in a direction generally parallel to a plane containingthe axes of said drums to produce maximum transverse stretching of theweb during passage of the web thereover.

3. Apparatus for stabilizing a paper web comprising a dryer sectionincluding two tiers of drying drums having at least two drums in eachtier and the drums of one tier staggered with respect to the drums inthe other tier, a web travel path passing around a first drum in onetier, a first drum in the other tier, a second drum in the other tierand then a second drum in the first tier, and a web straining device fortransverse stretching the web during its travel between the first andsecond drums of said other tier.

4. Apparatus as set forth in claim 3, wherein said web straining deviceis a bowed roll disposed between planes containing, respectively, theaxes of the drums in said one tier and the axes of the drums in theother tier, said roll being bowed in a direction to produce maximumtransverse stretching of the web during passage of the web thereover.

5. Apparatus as set forth in claim 4, wherein said web is in contactwith said roll through an angle in excess of References Cited UNITEDSTATES PATENTS 6/1881 Piper 34-116 XR 7/1951 Harlow 2663 U.S. Cl. X.R.26-63

